Newbie question about sets

I’m just curious if there’s any way to duplicate values in a set. After
quiz 108, I modified my submission so that it was a fully functional
game.
I then passed around my finished program to some of my coworkers who are
interested in ruby. After a few days, someone came back to me with a
bug,
and this appears to be the root cause of that bug.

irb(main):001:0> target = “stuff”
=> “stuff”
irb(main):002:0> a = target.split(//).sort
=> [“f”, “f”, “s”, “t”, “u”]
irb(main):003:0> require ‘Set’
=> true
irb(main):004:0> s1 = Set.new(a)
=> #<Set: {“f”, “s”, “t”, “u”}>

As it stands, if the word ffffuuuuussssstttt existed, it would be
considered
a subset of a. How do you avoid this using sets?

On Jan 15, 2007, at 1:57 PM, Jason M. wrote:

Set implements a collection of unordered values with no duplicates.

Yes, that implements sets as defined in math. What you wanted is
called “multiset”[*], though in my degree I never saw any of those
even mentioned.

– fxn

[*] http://mathworld.wolfram.com/Multiset.html

You shouldn’t really have to avoid this. The 6 letter word should be 6
unique letters, otherwise how would there be 6 letters for the user to
guess?

Dan

On 1/15/07, Jason M. [email protected] wrote:

irb(main):002:0> a = target.split(//).sort
=> [“f”, “f”, “s”, “t”, “u”]
irb(main):003:0> require ‘Set’
=> true
irb(main):004:0> s1 = Set.new(a)
=> #<Set: {“f”, “s”, “t”, “u”}>

As it stands, if the word ffffuuuuussssstttt existed, it would be
considered
a subset of a. How do you avoid this using sets?

Doh! first line of ri Set told me what I needed to know - that it’s not
really possible.

Set implements a collection of unordered values with no duplicates.

On 15.01.2007 14:36, Stefano Z. wrote:

reach 0.
def initialize
@arity[o] -= 1
if @arity[o] == 0
super(o)
@arity.delete o
end
end
alias << add
end

You can as well use a Hash as multi set:

irb(main):001:0> multi_set = Hash.new 0
=> {}
irb(main):002:0> multi_set[‘foo’] += 1
=> 1
irb(main):003:0> multi_set
=> {“foo”=>1}
irb(main):004:0> multi_set[‘foo’] += 1
=> 2
irb(main):005:0> multi_set
=> {“foo”=>2}
irb(main):006:0> multi_set[‘bar’] += 1
=> 1
irb(main):007:0> multi_set[‘bar’]
=> 1
irb(main):008:0> multi_set[‘foo’]
=> 2
irb(main):009:0> multi_set
=> {“foo”=>2, “bar”=>1}
irb(main):010:0> multi_set[‘foo’] -= 1
=> 1
irb(main):011:0> multi_set
=> {“foo”=>1, “bar”=>1}
irb(main):012:0> multi_set[‘xxx’]
=> 0

Of course this does not prevent values other than numbers as well as
negative numbers.

Ah, and btw, I’m not sure whether it’s a good idea to have a MultiSet
class inherit Set: after all Set /is (the special case of) a/ MultiSet -
not the other way round.

Kind regards

robert

On 1/15/07, Daniel F. [email protected] wrote:

You shouldn’t really have to avoid this. The 6 letter word should be 6
unique letters, otherwise how would there be 6 letters for the user to
guess?

Dan

So here’s what one of my coworkers sent to me:

Current score: 5900
Incorrect: 2
EIINSS
17 possible words left!
word:inn
Current score: 5990
Incorrect: 0

In this case, “inn”.split(//).sort would be s2, and @s1 would be
EIINSS.split(//). N did not appear in the word list twice, but the part
of
my code that said if s2.subset?(@s1) returned true because the actual
values
compared were
s2= Set: {“i”, “n”}
@s1 = Set: {“e”, “i”, “n”, “s”}
s2 is in fact a subset of @s1, but if Set allowed for multiple
non-unique
values (i.e. {“i”, “n”, “n”}) then it wouldn’t have been the case.

In the end, it doesn’t matter… I was just looking to make a game for
me
and my coworkers. Tech support is boring. But maybe finding all the
words
in seisin is more boring. I don’t know.

Answering to myself …

On Mon, Jan 15, 2007 at 10:29:11PM +0900, Stefano Z. wrote:

def delete(o)
  super(o)
  @arity[o] -= 1
  @arity.delete o if @arity[o] == 0
end

The above is of course wrong, elements get remove before their arity
reach 0.

=> nil # aargh, do I need to alias again in
# derived classes? that’s too bad …

Apparently so, alias makes a copy of the method :frowning:

Here is a better version:

require ‘set’
class MultiSet < Set
def initialize
super
@arity = {}
end
attr_reader :arity
def add(o)
super(o)
@arity[o] = 0 unless @arity.member? o
@arity[o] += 1
end
def delete(o)
@arity[o] -= 1
if @arity[o] == 0
super(o)
@arity.delete o
end
end
alias << add
end

On Mon, Jan 15, 2007 at 10:07:47PM +0900, Xavier N. wrote:

Yes, that implements sets as defined in math. What you wanted is
called “multiset”[*], though in my degree I never saw any of those
even mentioned.

I guess one can build them by herself on the following lines:

class MultiSet < Set
def initialize
super
@arity = {}
end
attr_reader :arity
def add(o)
super(o)
@arity[o] = 0 unless @arity.member? o
@arity[o] += 1
end
def delete(o)
super(o)
@arity[o] -= 1
@arity.delete o if @arity[o] == 0
end
end

but beware that the above is newbie’s code (and also utterly simplified
…) :slight_smile:

And by the way, why the above class does not work properly with <<
(which is an alias for add according to my set.rb) while it works
properly with add?

E.g.

irb(main):019:0> m=MultiSet.new
=> #<MultiSet: {}>
irb(main):020:0> m.add 1
=> 1
irb(main):021:0> m.add 1
=> 2
irb(main):022:0> m.arity[1]
=> 2 # so far so good

irb(main):023:0> m << 2
=> #<MultiSet: {1, 2}>
irb(main):024:0> m << 2
=> #<MultiSet: {1, 2}>
irb(main):025:0> m.arity[2]
=> nil # aargh, do I need to alias again in
# derived classes? that’s too bad …

TIA,
Cheers.

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